Download The Integration of Amateur Radio and 802.11

The Integration of Amateur
Radio and 802.11
Amateur Radio and 802.11 wireless networking —
a good fit for emergency message delivery.
Roderick D. Mitchell, KL1Y
I
ntegrating two distinct and otherwise autonomous systems can provide rewarding
results. There has been a lot of discussion
about the use of commercial wireless protocols in the Amateur Radio community. These
protocols, defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.11
standards, specify several wireless bands and
modulation schemes for local and wide area
networks. There are many possibilities with
great potential for using available low-cost
high-speed devices. Recently I had an opportunity to integrate Amateur Radio and 802.11.
The goal was to choose a project that was viable, worth while and feasible in regards to time
constraints. I chose the Winlink 2000 Paclink
network. Paclink is a component of the Winlink
2000 messaging system. The Paclink network
allowed me to integrate a wireless local area
network (WLAN) using 802.11b/g, a Paclink
e-mail server and an Amateur Radio system
into a single network. Each of the integrated
devices contains protocols and/or technologies
that allow it to interconnect with other systems
and devices in the network. Protocols are rules
that define how communications devices communicate in a network.
PO Box 35053
Fort Wainwright, AK 99703
[email protected]
The integration of various systems to
form a single diverse system is critical today.
Budget cuts that result in equipment and personnel shortages plague many organizations.
The ability to integrate non-profit organizations and leverage their experience is critical.
Amateur Radio Operators provide non-profit
services to the community. Now Amateur
Radio’s ability to support government and
non-governmental efforts during a disaster
has expanded. This added capability is due to
the integration of current automation and networking technologies with Amateur Radios.
Several Amateur Radio Operators (Vic Poor,
W5SMM, and Rick Muething, KN6KB) have
worked very hard to develop the Paclink messaging software that allow Amateur Radio to
integrate seamlessly with modern networking
equipment and e-mail clients such as Microsoft Outlook, Netscape and Outlook Express.
Table 1
Application Level Protocol Port
Assignments
Protocol
http
SMTP
POP3
TCP
Port
80
25
110
8000
The following sections describe the technical
details of the system that integrates Amateur
Radio and 802.11. This project supports the
implementation goals of high speed multimedia (HSMM) through the use of 802.11. This
integrated network easily integrates with the
Amateur Radio Internet (Hinternet).
Integrated Technologies Explained
The core technologies that form the
nucleus of this Hinternet project are radio
frequency (RF), IEEE standards, communications protocols and communications
applications and software.
Each of the core technologies has a place
in the Open Systems Interconnection (OSI)
model. OSI is a model for understanding and
developing computer-to-computer communications.1 The OSI model consists of seven
layers: physical, data link, network, transport,
session, presentation and application. See
Table 1. The following section describes the
integrated technologies of this project, their
protocols and their place in the OSI model.
OSI Model View of Integrated
Technologies
The physical layer of the OSI model converts the ones and zeros to electrical signals
1
Notes appear on page 32.
Figure 1 — Wiring diagram of integrated Amateur Radio and 802.11 network.
May/June 2007 27
Mitchell.indd 27
04/04/2007 8:25:53 AM
for transmission between devices.2 The data
link layer provides an error detection function. The network layer provides logical
addressing and routing of information on the
network. On the transport layer, error correcting techniques are employed.3 The session
layer allows provisions for data exchange
between applications as explained by Tuma
and Fajfar. Tuma and Fajfar explained the
presentation layer as the layer that ensures
that applications can communicate with each
other when the applications use different formats. The application layer is where application protocols reside in the OSI model.
The following sections describe functions
of the specific protocols and technologies
used in this project. The descriptions are
based on the protocol or technologies function in the OSI model. Table 1 provides a
quick view of the communications technologies used and their place in the OSI model.
Figures 3 through 6 show the elements of
the system.
Physical Layer
IEEE 802.11 at the Physical Layer
An 802.11b/g wireless access point (WAP)
provides LAN connectivity to wireless clients
equipped with 802.11b/g wireless network
interface cards (NICs). A high gain omni-
directional antenna is used for transmission
and reception of signals. 802.11 is a member of
the IEEE 802 family, a series of specifications
for local area network (LAN) technologies.
Figure 1 is a wire diagram. The diagram shows
the physical connectivity of the integrated
circuit. Figure 2 depicts interconnections from
a three dimensional perspective.
IEEE 802.3u at the Physical Layer
IEEE 802.3u is the standard also known
as Fast Ethernet. This project uses an SMC
small office/home office (SOHO) router. The
router provides connectivity at the physical
layer between the computer and WAP via
IEEE 802.3u interfaces.
Amateur Radio at the Physical Layer
The backbone (wide area network connectivity) of the network is dependent upon Amateur Radio at the physical Layer. Amateur Radio is used to move the data from the local area
network (LAN) to the Internet or other areas
outside the LAN. Amateur Radio technologies
and protocols used at this layer include: radio
frequency (RF), frequency modulation (FM),
TNCs and the AX.25 packet protocol.
AX.25 at the Physical Layer
The Amateur Radio packet protocol
AX.25 operates at the physical layer for
connectivity between two terminals. AX.25
assumes that both ends of the link are of the
same class.4 This class distinction is in regards
to data terminal equipment (DTE) and the
data communications equipment (DCE). With
AX.25 there is no DTE and DCE. Connectivity between the computer and TNC is over
serial cable using an RS-232 serial cable.
RS-232 at the Physical Layer
This network uses RS-232 connectivity
between the computer and TNC and between
the TNC and radio. RS-232 is a set of standards that specify three types of interfaces:
electrical, functional and mechanical.5 The
computer to TNC connection is a 9-pin D
shape connector on the computer side and
25-pin D shape connector on the TNC side.
The radio to TNC pin out for the 9-pin RS-232
connection and the 25-pin pin out are available
at the Kantronics Web site: www.kantronics.
com/documents/kpc3ppinout.pdf.
Coaxial Cable at the Physical Layer
Coaxial cable is used between the transceiver and the antenna. RG-8/U is used for
this application. Some versions of RG-8/U
have relatively low loss. We selected one
that had a loss of approximately 1.8 dB per
Table 2
OSI Reference Model with Technologies Used in the Integrated Amateur Radio and 802.11 Networks
OSI Layer
Application Layer (7)
Presentation Layer (6)
Session Layer (5)
Transport Layer (4)
Network Layer (3)
Data-Link Layer (2)
Physical Layer (1)
Protocol or Technology
SMTP, POP3, DHCP
B2F
TCP/IP (Sockets)
TCP, SMTP (Port 25), POP3 (Port 110), HTTP (Port 80)
IP and Router
802.11, 802.3u, AX.25, KISS, Switch
AX.25, RF, RS-232, IEEE 802.3u, IEEE 802.11, Coaxial Cable (RG-8/U), UTP Cable
Figure 2 — Interconnections of integrated network.
28 May/June 2007
Mitchell.indd 28
04/04/2007 8:26:24 AM
100 feet over 144 to 148 MHz. With our
50 feet, power loss is about 0.7 dB.6
UTP Cable at the Physical Layer
Unshielded twisted pair (UTP) cabling
is used to interconnect the router, WAP and
server. UTP is less expensive than its shielded
(STP) counterpart. STP provides the best
immunity to stray RF interference. The short
lengths of UTP have proved reliable in this
project. The UTP cable consists of four insulated pairs of wire. Wires 1, 2, 3 and 6 are used
for transmission and reception of signals.
style networking to radio links. In a similar
way that Ethernet operates, 802.11 uses a carrier sense multiple access (CSMA) scheme to
control access to the transmission medium.
IEEE 802.11 uses carrier sense multiple
access collision avoidance (CSMA/CA) rather
than the carrier sense multiple access collision
detection (CSMA/CD) scheme used by 802.3
(Ethernet). CSMA/CA attempts to avoid col-
lisions. CSMA/CD detects collisions, stops
transmitting and then retransmits the data.
IEEE 802.2 at the Data Link Layer
IEEE 802.11 uses the IEEE 802.2 encapsulation. The logical link control (LLC)
sublayer protocol allows the 802.3 and
802.11 protocols to carry multiple, logical
sub-network traffic of each protocol over the
LARRY LEDLOW JR, N1TX
Data Link Layer
Network Switch at the Data Link Layer
Switches are connectivity devices that
make efficient use of bandwidth. Switches
allow devices to establish a direct connection
to another port on the switch. This is in contrast to hubs that broadcast data to all ports.
The switch in this network implementation
provides connectivity for the WAP and server.
Other LAN computers or, a printer, may be
attached to the switch as the need arises. The
switch interprets media access control (MAC)
address information to determine where to forward packets it receives.7 The MAC address
is a special address that is burned on the NIC
during the manufacturing process. Each MAC
address is unique. The switch, dynamic host
control protocol (DHCP) server and router are
all integrated in the SMC router housing.
IEEE 802.11 at the Data Link Layer
The definition of 802.11 functions at the
MAC sublayer of layer 2 of the OSI model
stated that “802.11 allows for mobile network
access; in accomplishing this goal a number
of additional features were incorporated into
the MAC.”8 As a result the 802.11 MAC may
seem baroquely complex compared to other
802 MAC specifications”.
IEEE 802.11 is not a far departure from
other 802 standards. 802.11 adopted Ethernet-
Fig 3 — Rod, KL1Y, explaining the possiblities that exist when using 802.11 with Amateur
Radio. The two Boy Scouts are Michael Walsh (closest to Rod) and Jackson Drew.
Figure 5
— Breannah
Jayde Mitchell
(Rod’s daughter)
prepares a
message for
transmission
from a wireless
enabled
computer on
the integrated
network.
Figure 4 — Denise Mitchell, KL1OP (Rod’s wife), sits at the
operating position and monitors activities on the Paclink server.
May/June 2007 29
Mitchell.indd 29
04/04/2007 8:26:57 AM
same physical medium such as the LAN.9
The LLC sublayer provides an interface
with the network layer protocols. The LLC
sublayer is responsible for the ordered delivery of frames, including retransmission
of missing or corrupt packets and for flow
control (moderating flow so that one system
does not overwhelm the other).10
IEEE 802.3u at the Data Link Layer
IEEE 802.3u (Ethernet) is used to provide
connectivity between the Paclink server and
WAP via the SOHO router. IEEE 802.3u
specifies a standard capable of sending data
at 100 Mbps (Newton, 2005, p 31).11 At
layer 2 Ethernet uses the CSMA/CD media
access control.
The specific layer 2 functions of Ethernet
include encapsulation and de-encapsulation
of user data, media access management, collision detection and handling data encoding
and decoding and finally, channel access to
the LAN medium.12
Amateur Radio at the Data Link Layer
Amateur Radio protocols at layer 2 are
AX.25 and Keep it Simple Stupid (KISS). The
AX.25 protocol functions at both the physical
and data link layers. KISS functions only at
the data link layer. At layer 2, AX.25 encapsulates the e-mail messages for transmission
over the air through radio frequencies. AX.25
ensures that compatibility exists between two
Amateur Radio stations at layer 2.
The data rate between the TNC and radio is
only 1200 bps. This provides a throughput of
1200 bps across the backbone link. The robustness and stability of this protocol are sufficient
enough to make up for the low throughput.
These qualities are suitable for text messages
and small (30 kB) attachments.
KISS (Keep It Simple Stupid) is the layer 2
protocol used for connectivity between the Paclink server and the TNC. This connectivity is
over an RS-232 serial port. The KISS protocol
on the TNC gives the Paclink server complete
control over and access to the contents of the
HDLC (high level data link control) frames
transmitted and received over the air.13
The TNC simply converts between synchronous HDLC, spoken on the half-duplex
radio channel, and a special asynchronous, full
duplex frame format spoken on the Paclink
server/TNC link. Every frame received on the
HDLC link is passed intact to the host once it
has been translated to the asynchronous format; likewise, asynchronous frames from the
host are transmitted on the radio channel once
they have been converted to HDLC format.14
The KISS protocol uses p-persistence. Ppersistence causes the TNC to wait for an exponentially distributed random interval after
sensing that the channel has gone clear before
attempting to transmit. With proper tuning
of the parameters p and SLOTTIME, several
stations with traffic to send are much less
likely to collide with each other when they
all see the channel go clear. One transmits
first and the others see it in time to prevent
a collision. This is similar to the CSMA/CA
technology used by 802.11.15
Network Layer
Network Router at the Network Layer
The network layer of this integrative project employs the use of a router. The router is
the gateway to the LAN and allows remote
clients to access the e-mail server. The router
forwards the packets throughout the LAN/
WLAN based on their logical addresses.16
The network router used in this implementation is an SMC small office/home office
(SOHO) router. This router uses logical addresses (IP addresses) to direct data between
networks or segments.17 The router used in
this project has a WAN port that is connected
to another network (separate broadcast domain). Nodes in the same broadcast domain
can communicate with one another without
passing data through a router.
Internet Protocol (IP) at the Network Layer
IP version 4 (IPv4) at the network layer
of the OSI model is used for this project.
The Paclink server and the wireless clients
communicate by IP. The Paclink server is
assigned a static IP address and the wireless
clients may be addressed by dynamic or
static configuration. The Paclink server is
the e-mail gateway and provides access to
the AX.25 channels. The WAP communicates with the Paclink server via the IP. Each
wireless client, the WAP and Paclink use a
32 bit IP address. The addresses are within
the same broadcast domain (network). The
WAP has a management IP address that is in
a separate broadcast domain.18
The Paclink server is the gateway device
that provides connectivity between the IP
network and the AX.25 network. The network layer IP datagram is passed through the
gateway to the data link layer AX.25 protocol
that resides on the Paclink server (gateway)
for encapsulation and transmission through
the Amateur Radio portion of the network.
This process works in reverse as the frames
come in through Amateur Radio and reach
the TNC, then the gateway (Paclink Server)
for transmission to the wireless clients.
Transmission Control Protocol (TCP) at
the Transport Layer
TCP is the transport layer end to end protocol. TCP provides reliable, sequenced, and
unduplicated delivery of bytes to users on the
wireless LAN (WLAN) and LAN.19
TCP is a connection-oriented protocol.
TCP first establishes a connection between
the two systems that intend to exchange data.
TCP formats segments for the network layer
by breaking the segments into packets that
are the appropriate size for the network.20
TCP assigns each packet a sequence number.
The packets are reassembled at the distant
station in accordance with their sequence
numbers. TCP uses a checksum to verify the
accuracy of the message. If the checksum is
accurate the recipient sends an acknowledgment (ACK). If the checksums do not match,
the recipient asks the sender to resend the
message.21
Figure 6 — The components of the integrated network are pictured left to right:
Astron power supply, MFJ power strip, Yaesu FT-8800 transceiver with KPC3+
TNC sitting on top, Winbook laptop with Paclink AGW, Paclink Post Office and
AGW Packet Engine software installed. To the right of the server is the SMC
router and behind the router is the DWL-2100AP modified by NETKROM.
30 May/June 2007
Mitchell.indd 30
04/04/2007 8:27:31 AM
TCP uses ports to establish communications between the various application layer
protocols used in this network. Ports are a
logical point of connection in the context of
TCP. TCP uses port values in the range of
0 to 65,535. The application level protocols
and ports used in this network are shown in
Table 1.
HTTP (application level protocol) port
80 is used for management of the WAP and
router. SMTP port 25 and POP3 port 110 are
used by the e-mail clients for messaging. On
the client computer, additional ports are used
at random to establish a connection on the
server with the ports listed above. This was
revealed during an analysis using an Ethereal
protocol analyzer. Port 8000 is used to connect
Paclink AGW to the AGW Packet Engine.
TCP/IP Sockets at the Session Layer
TCP/IP sockets are used at the Session
layer of the OSI model. At this layer the
logical links are bound and unbound between
application layer protocols (users of service).
The session layer maintains and controls the
dialogue between the users of the service.22
In TCP/IP the socket number is the joining of the senders’ (or receivers’) IP address
and port numbers for the service being used
(Example: 192.168.25.38:80). The combined
IP address and port number identifies the
unique connection in the network.23
B2 Forwarding (B2F) Protocol at the
Presentation Layer
B2F is used at the presentation layer for
preparing messages for transmission over the
single channel Amateur Radio.
B2F describes an alternate “automatic
only” addressing and protocol scheme for
delivering messages within the Winlink 2000
system. Poor, W5SMM, et al explained that
“messages consist of three parts: header;
body and attachments.”24 All parts of the
message are combined into a single file that
is compressed by B2Compress.exe, the B2F
protocol compression program, as a unit
before transmission.
Application Layer
SMTP at the Application Layer
The simple mail transfer protocol (SMTP)
is used with the Paclink server. SMTP facilitates the outgoing message transfer function
for e-mail clients. If an e-mail program such
as Outlook Express is used on the Paclink
server, the outgoing mail field is set to LOCALHOST. The WLAN and LAN client e-mail
programs’ outgoing mail field is set to the IP
address of the Paclink server.
Post Office Protocol 3 (POP3) at the
Application Layer
The POP3 service is provided by the
Paclink server. The server facilitates the in-
coming message transfer function for e-mail
clients. If an e-mail program is installed on
the Paclink server this e-mail program’s incoming mail field is set to LOCALHOST. The
WLAN clients’ e-mail program’s (Outlook,
Netscape, etc...) incoming mail field is set to
the IP address of the Paclink server.
DHCP at the Application Layer
DHCP (Dynamic Host Configuration
Protocol) is an application layer protocol
(Dean, 2006).25 DHCP is used in this network to provide automatic IP addressing
for computers that connect to the integrated
network through the WAP or directly to the
switch. One of the many functions of the SMC
small office/home office (SOHO) router is the
DHCP server function. The Paclink server is
not setup for DHCP. DHCP addresses could
change automatically as leases expire therefore it is better to setup the Paclink server with
a static IP address. Clients require seamless
connectivity to the Paclink server. Changing
the IP address on an inconsistent basis would
disrupt the seamless connectivity. Dynamically assigning addresses to clients is a good
idea because it lightens the administrative
duties of the network administrator.
Software Packages Explained
The software packages used in this project
provide connectivity and driver functions to
facilitate the transfer, compression of data and
transmission of data over the radio waves.
The software used by the integrated Amateur
Radio and 802.11 project include AGW Packet
Engine, Paclink AGW, Paclink Post Office and
the e-mail program, Outlook Express.
AGW Packet Engine
AGW Packet Engine is the TNC driver
that resides on the Paclink server. The packet
engine interfaces the TNC and Paclink AGW
software. AGW Packet Engine is setup in KISS
mode to communicate with the TNC. The
packet engine controls the radio data rate and
issues all commands required to facilitate communications between Paclink, the TNC, and
radio. AGW Packet Engine creates channels
with communications ports for Paclink AGW.
These pre-defined channels allow Paclink to
send data over the radio via the TNC.
Paclink AGW
Paclink AGW communicates with Paclink
Post Office and AGW Packet Engine. Paclink
AGW formats the messages for delivery
by compressing the message with the B2F
protocol. Paclink AGW has an open dialog
box that allows the network administrator
or radio operator to monitor the connection,
compression and message dialog between
the Paclink server and the PMBO. In
addition to other functions provided by
Paclink AGW, AX.25 functions and
features are provided by this software.
Paclink Post Office
The integrated Amateur Radio and 802.11
network uses Paclink Post Office as a component of the Paclink server. Paclink Post Office
is the program required to provide connectivity between Paclink AGW and the user’s
e-mail program. Paclink Post Office provides
the POP3/SMTP mail server functions.
In this installation Paclink Post Office
uses the Amateur Radio call sign KL1Y for
the Paclink site. Paclink Post Office may be
configured for use on the local machine and
LAN. The SMTP port number used is 25 and
the POP3 port number is 110. Paclink Post
Office listens on these ports for connection
requests from e-mail programs.26 When each
e-mail program requests to connect to the
POP3 server for the purpose of sending and
receiving e-mail, the Paclink POP3 server
validates the username and password.
The use of tactical addresses and the ability to use a common e-mail application are
two key aspects of this network that allow
the Amateur Radio community to seamlessly integrate with supported agencies and
provide quick and reliable support. Tactical addresses are non-Amateur Radio call
signs. An example of a tactical address is:
[email protected].
E-mail Program
This project uses Microsoft Outlook and
Microsoft Outlook Express. It is possible to
install and use any e-mail program capable
of POP3 configuration. Messages sent to
targeted recipients are viewed by any e-mail
program capable of viewing text messages.
The Support Team
John Champa, K8OCL, HSMM Chairman,
was instrumental in providing advice and mentorship in developing this document. Many
local Amateur Radio operators supported the
development of this local implementation.
The operators readily provided logistics support and technical expertise. Linda Mullen,
AD4BL, obtained a grant to purchase the
amateur gear used in the project, Kody Moore,
KLØRN, hand made the interface cables that
connected the radios to the TNC,
Larry Ledlow Jr, N1TX, provided guidance
as my mentor during the entire project. Larry
devoted countless hours to reading drafts and
the discussion of technical details.
Jerry Curry, KL7EDK, was instrumental
as the Participating Mailbox Office (PMBO)
Operator and packet expert. Dan Wietchy,
KL1JP, was helpful in providing feedback
and advice for the original paper.
Conclusion
This integrated network provides connectivity to the Amateur Radio network
May/June 2007 31
Mitchell.indd 31
04/04/2007 8:27:59 AM
through 802.11. The use of 802.11 in this
scenario allows connectivity without wires.
This extension of the radio network provides
a convenient messaging system that can be
quickly deployed.
In backbone architectures the VHF Amateur Radio network has proven much more
reliable than 802.11 networks despite the low
throughput of the Amateur Radio network.
The use of 802.11 is not out of the question
for the WAN links. An 802.11 WAN network
is highly dependent upon line of sight connectivity with minimal obstruction.
Notes
1
T. Dean, Network+ Guide to Networks,
4th Edition, Boston: Course Technology, 2006.
2
See Note 1.
3
T. Tuma and I. Fajfar, “Hands on approach to
teaching the basic OSI reference model.” International Journal of Electrical Engineering
Education, 37(2), 157, 2000.
4
W. Beech, D. Nielsen and J. Taylor, AX.25 Link
Access Protocol for Amateur Packet Radio,
Revised Edition, Tucson Amateur Packet
Radio Corporation, 1998.
5
H. Newton, Newton’s Telecom Dictionary, 21st
Edition. San Francisco: CMP, 2005.
6
West Penn Wire. RG-8/U Coaxial Cable Flexible Design, 2005. www.westpenncdt.com/
pdfs/RF_Transmission_50-OHM_cables/
808F.pdf.
7
See Note 1.
8
M. Gast, 802.11 Wireless Networks, 2nd Edition, Sebastopol, CA, O’Reilly Media, Inc,
p 14.
9
D. Spohn, Data Network Design, 2nd Edition,
New York, McGraw-Hill, 1997, p 255.
10
M. Myers. Managing and Troubleshooting
Networks. Boston: McGraw-Hill, p 50.
11
See Note 5, p 31.
12
See Note 8, p 260.
13
M. Chepponis, K3MC, and P. Karn, KA9Q,
KISS Protocol, www.ax25.net/kiss.htm.
14
See Note 13.
15
See Note 13.
16
See Note 1.
17
See Note 1.
18
See Note 5, p 444.
19
See Note 5, p 828.
20
See Note 5, p 829.
21
See Note 5, p 829.
22
See Note 5, p 755.
23
See Note 5, p 778.
24
V. Poor, W5SMM, H. Kessler, N8PGR,
G. Muething, KN6KB, S. Waterman, K4CJX,
winlink.org/B2F.htm.
25
See Note 1.
26
G. Muething, KN6KB, and V. Poor, W5SMM,
“Paclink AGW a Modern AX.25 WL2K Packet
Client Compatible with POP3/SMTP Clients,”
2005.
Additional References
The ARRL Handbook for Radio Communication, 2007 Edition. Available from your ARRL
dealer or the ARRL Bookstore, ARRL order
no. 9760. Telephone 860-594-0355, or tollfree in the US 888-277-5289; www.arrl.org/
shop/; [email protected].
R. Bass, J. Potter, K. McGinnid, and T. Miyahira,
“Surveying Emerging Trends in Emergencyrelated Information Delivery for the EMS
Profession,” Topics in Emergency Medicine,
26(2), 93-102.
WANTED: C++ PROGRAMMER
We need a part time C++ programmer who likes to work at home but lives in the Orange
County/Los Angeles area. We need to automate our test procedures, which involve RF
transmitters and receivers to determine if production products pass or fail. Tests include
determining RF output, current consumption, PLL lock range, frequency accuracy, and
receiver sensitivity by checking each section with a fully or semi-automated test program.
We need the following:
-Someone with experience writing Visual C++ programs allowing the PC to control the test equipment
with RS-232 and or GPIB.
-You need to be familiar with RF test equipment such as spectrum analyzers, oscilloscopes, signal
generators, and frequency counters.
-Be familiar with troubleshooting of RF and digital circuits.
-Be able to control relays, switches, etc. through PC I/Os with Visual C++.
-Have TCP/IP programming experience with Visual C++.
-Have CGI programming experience in any language.
-Robotic experience a plus.
-We would like to see examples and or samples of your past work.
E-mail: [email protected]
S. Bender, Producing the Capstone Project,
Dubuque, IA: Kendall/Hunt.
H. Berghel, “Wireless Infidelity I: War Driving,”
Communications of the ACM, 47(9), 21-26.
F. Block and M. Pursley, “A Protocol for Adaptive
Transmission in Direct-Sequence SpreadSpectrum Packet Radio Networks,” IEEE
Transactions on Communications, 52(8),
1388-1396.
M. David, “ARRL’s Role in Rescue Offers Lessons for Future,” Electronic Design,19.
Kantronics KPC-3+ Port Pinout Information, www.kantronics.com/documents/
kpc3ppinout.pdf.
T. Lammle and A. Barkl, Cisco Certified Design
Associate second edition. San Francisco:
Sybex.
L. Luna, “Getting Back Backhaul Costs,”
Telephony, 246(24), 10-12.
D. Rickie, “A Three-dimensional Framework for
Information Technology Solutions,” IBM Systems Journal, 39(2), 336.
C. E. Strangio, The RS-232 Standard, www.
camiresearch.com/Data_Com_Basics/
RS232_standard.html.
B. Waldo, “Information Technology: Strategies
for Success,” Nursing Economic$, 16(1),
33-43.
K. Schwalbe, Introduction to Project Management, Course Technology, Boston.
Rod Mitchell, KL1Y, became a licensed
Amateur Radio operator in September 2000.
He is also a member of the Army MARS program and is licensed as ALM7AQ. He holds
a Master of Science in Information Technology from Capella University. He also holds
an FCC General Radiotelephone Operator
License, is a Cisco Certified Network Associate, Cisco Wireless LAN Support Specialist,
Foundry Networks Certified Network Engineer, CompTIA A+ and CompTIA Network+
certifications.
He currently is serving his 21st year in
the US Army and holds the rank of Chief
Warrant Officer Four (CW4). His present
assignment is Officer-In-Charge of the Local
Network Operations and Security Center at
Fort Wainwright, Alaska. He has recently
accepted an appointment as Director, US
Army MARS — Alaska.
Rod’s previous positions include
Communications and Electronics Integration Officer for the 172nd Stryker
Brigade, US Army Alaska, Avionics Maintenance Officer-In-Charge, Communications
and Electronics Maintenance Officer with
82nd Signal Battalion, 82nd Airborne Division, 514th Signal Company, 35th Signal
Brigade and 520th Maintenance Company,
South Korea. Rod served as a Special Electronics Devices Technician and Instructor
with the US Army. Rod’s first opportunity
to operate radios was while assigned as a
radio telephone operator (RTO) with the 4th
Infantry Division. Rod is an adjunct faculty
member with the University of Alaska Fairbanks, Tanana Valley Campus, Information
Technology Department.
32 May/June 2007
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Network/Data Layer
Messaging Protocol for
Stand-Alone, Free-Field
Communications Systems
The author proposes protocols and data formats for a
self-organizing network of stations to pass messages.
Lindsay J. Robertson, ZL2LJR
Abstract
Protocols and data formats are proposed
that will allow a completely self-organizing
network of peer stations using free-field,
physical-layer communications to pass message packets from an originating station to
a designated destination station at arbitrary
distance, needing no other equipment or
systems. The proposed system is presented
in enough detail to allow implementation,
but most importantly, the paper establishes
some general principles that can be extended
and developed as required.
Briefly, a datagram header format that
contains geographical location and a local identifier of the destination station is
proposed: peer stations build up internal
lists of ID’s and locations of other peer
stations that they can “hear” — and hence
each station that progresses a datagram is
able to automatically select an optimum
station to which the transient datagram may
be passed. Simple protocols are proposed
for authenticating and verifying datagram
transfer, for rerouting datagrams to ensure a
high probability of delivery, and for purging
of datagrams that are successfully passed
towards their final destinations. An “open”
approach that encourages user control and
further optimization is proposed. This is different from present Mobile Ad-hoc Network
(MANET) protocols, and it also differs in
several aspects from current geographic
routing proposals and current radio packet
transfer systems.
Need for Robust, Free-Field Network
Layer System
Life without instant, reliable communication is just about inconceivable — we simply
assume reliable communication via the Internet, cellular and “landline” phone services.
Yet a review of existing systems shows
that only the long-range point-to-point HF
radio system is both independent of a “wired
backbone” and capable of long-range messaging. Although workable, the point-topoint HF radio system has limited reliability.
(It depends upon ionospheric conditions
between two stations, and is a highly inefficient use of bandwidth.)
Reliance upon wired communication backbones represents a significant vulnerability. To
appreciate the issue, one only has to consider
how useless a cell-phone handset is, without
the cell-phone nodes and inter-node routing
systems. A news item “The Backhoe: A Real
Cyberthreat” describes this issue eloquently.1
The existing systems therefore do not
adequately address any of the following
situations:
• Cases where a large number of users (each
with limited power) want to exchange
messages over long distances, without
excessive use of bandwidth.
• Cases where the only open bands are not
available to a particular station (stations
of limited power, or only VHF.
• A user (particularly a VHF/UHF user) who
lives in a geographically remote location,
such as at the end of a long valley.
• The aftermath of a natural disaster, (or delib-
[email protected]
1
Notes appear on page 38.
erate sabotage) when a user is affected by
disruption of either “last mile” or backbone
transmission lines, or the loss of third party
communication facilities. See Note 1.
• The aftermath of software errors (or attacks) upon a system that relies on a
hardwired backbone.2, 3
• A user who lives in a region in which
backbone communication facilities are
operated by authorities whose oversight
is unwelcome.
Situations of these types, and the lack of
adequate solutions, represent the “need” that
is addressed in this paper.
Existing Systems
Classification of Existing Systems
Before considering any proposed “new”
system, it is essential to review systems already in existence. Classifications of network
systems have been published before, however
these have generally been limited to relatively
narrow fields. For the purposes of this paper,
a very broad approach is taken, and the following categories are proposed:
“Wired” Systems. For these systems, all
nodes are hard-wired, and for each route
segment, a router selects the next destination
node and switches the packet to that node.4
(See the referenced text, starting on page
405.) Examples include the Internet, and
landline telephones. These offer efficient,
high-speed communication, but are totally
dependent upon the “wired” connection,
and vulnerable to either physical disruption
of wired “backbone” (see Note 1), and electronic disruptions (see Notes 2 and 3).
Wireless Neighborhood Networks. These
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